This invention resides in the field of textile processing, and also in the use of enzymes.
Fibers and fabrics of cotton and other textile materials are not suitable for dyeing or finishing in their raw state since they have low wettability, as evidenced by contact angles in the range of 93xc2x0 to 95xc2x0, and low water retention, typically on the order of 0.15 mL of water per mg of fiber or less. In cellulose-based fibers, these characteristics are attributed to the non-cellulosic impurities in the materials. The impurities are typically of a wax-like or oily nature. Removal of these non-cellulosics is achieved in textile processing by alkaline scouring, which is performed by immersing the materials in boiling caustic solution. Alkaline scouring consumes both time and energy, and produces waste water containing considerable quantities of salts after the used alkali has been neutralized.
Synthetic fibers such as polyester have similarly high water contact angles, low wettability and minimal water retention. In contrast to cellulose-based fibers, these effects are not caused by the presence of impurities, but are rather an inherent characteristic of the polyester surface. If it is desired to dye the polyester fabric, the situation is further complicated as standard polyester fibers, and fabrics made from these fibers, have no reactive dye sites. Polyester fibers are typically dyed by diffusing dyes into the amorphous regions of the fibers. Methods have also been developed for improving dye uptake and other properties of polyester by modifying the surface of the fibers.
The modification of the surface of polyester fibers by physical or chemical means is known. For example, anionic sites have been added to polyester fibers using 5-sulfoisophthalate as a method to make polyester fibers reactive towards cationic dyestuffs. Similar to the procedure followed with cellulosic fibers, the surface of polyester fibers has been modified by alkaline treatment of freshly extruded fiber to improve comfort and increase water sorption. Disclosures of these treatments are found in U.S. Pat. No. 5,069,846 and U.S. Pat. No. 5,069,847. Alkali treatment of polyesters, however, often results in a weakening of the fiber strength.
Enzymes have been used in the textile industry and various uses are disclosed in the literature. The enzymes commonly used include amylases, cellulases, pectinases and lipases. In typical applications, amylases are used to remove sizing agents (e.g., starch), cellulases are used to alter the surface finish of, or remove impurities from, cotton fibers and lipases are used to remove fats and oils from the surface of natural fibers (e.g., cotton, silk, etc.).
Amylases are used to remove sizes from fabrics, the sizes having been applied to the yarns prior to weaving to prevent the warp yarns from damage during weaving. The size is removed prior to further finishing processes such as bleaching or dyeing. The most common sizing agent is starch. Examples of commercially available xcex1-amylases include AQUAZYM(copyright) and TERMAMYL(copyright) (Novo Nordisk A/S).
Enzymes have also been used for denim garment finishing, to achieve soft hand and the fashionable worn look traditionally obtained by stone-washing and acid washing. The enzymes used for this purpose are microbial cellulases.
Another use of cellulases in the treatment of cotton is disclosed by Rxc3x6ssner, U., xe2x80x9cEnzymatic degradation of impurities in cotton,xe2x80x9d Melliand Textilberichte 74:144-8 (1993) (Melliand English 2/1993: E63-E65). The cellulases in the Rxc3x6ssner disclosure were used as a replacement for alkali. The cellulases were used in combination with surface-active agents, whose inclusion was apparently thought necessary to achieve wettability. The treatment solutions also contained an unspecified buffer. The enzyme reactions were terminated by washing at boil for an unspecified time. The stated purpose of the enzyme treatment was to improve the quality of the finished goods by dehairing, smoothing and internal softening. No mention is made of permanently improving the wettability or absorptivity of the goods.
Pectinases have been used to remove polysaccharide impurities from fibers such as ramie, flax, hemp and jute by incubating the fiber with an aqueous solution of the enzyme at, for example, 40xc2x0 C. at a pH of 4.7 for 24 h (JP 4289206).
The use of lipases to remove oily stains from garments is known in the detergent art (e.g., U.S. Pat. No. 4,810,414). Lipases have also been used in textile finishing. For example, Petersen discloses treating natural fibers with lipases to remove residual triglycerides and other fatty materials. The process is also useful for removing oil or ester coatings that have been added during processing (WO 93/13256). No mention is made in Petersen of using lipases to alter the properties of a polyester fiber by cleaving structural ester bonds at the surface of the fiber. Lund, et al. disclose the use of lipases in organic solution to modify with carboxylic acids the surfaces of certain fabrics. The lipases are used to form esters between the carboxylic acids and fibers which have reactive hydroxyl groups at their surface (WO 96/13632).
The alkali processing of fibers using NaOH has several inherent disadvantages. The use of large quantities of boiling aqueous sodium hydroxide is undesirable for reasons of safety, convenience and also for the volume of waste salt which is produced following neutralization of the alkali bath. The use of hot alkali to treat fibers also results in damage to the fibers which lessens their strength and durability. Thus, a means for treating fabrics to increase their wettability and absorbency which avoided the use of an alkali bath would constitute a considerable advance in the field of textile processing. Quite surprisingly, the instant invention provides such a means.
It has now been discovered that water wettability and absorbency in textile fibers can be increased by treatment with any of four classes of enzymes. Pectinases, cellulases, proteases and lipases, either alone or in combination, and either as the sole treatment step or following a brief boiling treatment in neutral water, have been found to produce water wettability and whiteness that are either equivalent or superior to the wettability and whiteness achieved by alkaline scouring. The enzymes eliminate the need for the high pH entailed in alkaline scouring, and avoid alkaline discharges. The enzymes can also eliminate the need for surfactants and the associated costs, and the enzyme treatment can be conducted at moderate temperatures. It has in fact been found that the enzyme treatment of fabrics without surfactants lowers the contact angle considerably and the resulting fabrics can absorb about 25% to 40% more water than fabrics that are treated by alkaline scouring.
Thus, in one embodiment, the instant invention provides a method of altering water wettability and absorbency in textile fibers, comprising treating the fibers with an enzyme in an aqueous medium, the enzyme being a member selected from the group consisting of pectinases, cellulases, proteases, lipases, and combinations, thereof and the aqueous medium being substantially free of surface active agents.
It has now been found that pectinases and cellulase in combination are particularly useful in increasing the water wettability and water retention of cotton fabrics. Thus, in a second embodiment, the invention provides a method of increasing water wettability and absorbency in cotton fibers, comprising treating the cotton fibers with an enzyme mixture further comprising a pectinase and a cellulase, in an aqueous medium.
In another embodiment, lipases have been shown to dramatically improve the wettability and water retention of aromatic polyester fibers while, in contrast to the techniques of the prior art, causing a minimal loss of fiber weight and strength. Therefore, in yet another embodiment, the instant invention is a method of altering the physical properties of polyester fibers, comprising treating the polyester fibers with an aqueous solution of a lipase to produce polar groups on the fiber. The polar groups on the fiber can modify physical properties of the fiber including its wettability and absorbency. Within the scope of this embodiment of the invention is the use of surfactants as a component of the reaction medium.
These and other features and advantages of the invention will become apparent from the description that follows.